A method for inverting ship speed based on the infrared polarization characteristics of wakes

Abstract

A method for ship speed inversion based on the infrared polarization characteristics of wakes is presented. This method belongs to the field of speed assessment technology based on optical technology. It solves the problem that existing detection methods are only applicable to wake infrared intensity detection under conditions of significant temperature difference between the wake and the sea surface, and cannot be applied to wake detection under complex conditions to analyze ship speed. By utilizing the difference between the infrared polarization characteristics of the ship's wake and the surrounding sea surface, the infrared polarization characteristics of the wake are detected and analyzed, improving the visibility and identification of the ship's wake. A sea surface ship wake infrared polarization transmission model based on the infrared linear polarization degree of the ship's wake is constructed. The correlation mechanism between ship speed and infrared polarization characteristics is explained through theoretical analysis, and the speed inversion result corresponding to any original infrared polarization image of the ship's wake on the sea surface is further obtained through inversion.

Description

Technical Field

[0001] This invention belongs to the field of ship speed assessment technology based on optical technology, specifically relating to a ship speed inversion method based on the infrared polarization characteristics of the wake. Background Technology

[0002] As a vital carrier of the maritime transport system, the classification of ships and the real-time monitoring of their navigation attitude are crucial aspects of international maritime supervision. The characteristics of the wakes generated by ships during navigation are an important basis for identifying ship targets in marine remote sensing technology and are also considered an effective way to invert ship dynamic parameters. In the field of military reconnaissance, infrared radiation-based detection methods have long been used for ship identification. This technology achieves detection and location by capturing the difference between the target's thermal radiation and that of the sea surface. However, when the thermal radiation of a ship's wake is close to the ocean background radiation, or when the target is in an area affected by solar flare reflection interference, traditional thermal contrast detection methods are prone to technical bottlenecks such as reduced signal-to-noise ratio and blurred target features, which restricts the environmental adaptability of the detection system.

[0003] When a ship travels at a constant speed in the ocean, the interaction between the ship and the seawater creates a stable V-shaped Kelvin wake on the surface. The duration and coverage of this wake are significantly greater than that of the ship itself.

[0004] Furthermore, the characteristics of the contrail itself are very obvious, making Kelvin contrails easier to detect than the ship itself. Additionally, due to the churning of the hull, seawater from the bottom rises to the surface, and the temperature stratification of the seawater means that the temperature of the bottom seawater is lower than that of the surface, thus making the infrared characteristics of the contrail significantly different from the surrounding sea surface.

[0005] Meanwhile, both the infrared radiation emitted by the wake itself and the reflection of radiation from the surrounding environment undergo polarization, thus distinguishing the infrared polarization characteristics of the wake from those of the surrounding seawater. Therefore, infrared polarization detection can fully utilize information such as the surface roughness and refractive index of the wake, effectively suppressing background and improving the wake detection rate.

[0006] However, current ocean detection methods primarily rely on infrared radiation intensity detection, which mainly utilizes the temperature difference between the target and the background for identification. This approach is only suitable for situations where there is a significant temperature difference between the wake and the sea surface. When the temperature difference between the target and the background is small, infrared detection methods based on radiation intensity exhibit significant limitations and cannot guarantee the accuracy and efficiency of wake identification. Summary of the Invention

[0007] To address the problem that existing detection methods are only applicable to wake infrared intensity detection under conditions of significant temperature difference between the wake and the sea surface, and cannot be used for wake detection under complex conditions to determine ship speed, this invention provides a ship speed inversion method based on wake infrared polarization characteristics. The method includes the following steps:

[0008] S1. Use 3D modeling software to create a 3D model of the fluid domain of the ship's wake on the sea surface;

[0009] S2. Establish a height field model of the ship's wake on the sea surface, use a three-dimensional model of the fluid domain of the ship's wake on the sea surface to simulate the ship's navigation, and use CFD simulation to obtain numerical simulation results of the height field of the ship's wake at different speeds.

[0010] S3. Combine the height field model of the wake of a ship on the sea surface with the micro-element polarization bidirectional reflection distribution function PG model to establish an infrared polarization transmission model of the wake of a ship on the sea surface.

[0011] S4. Substitute the numerical simulation results obtained in step S2 into the infrared polarization transmission model of the wake of a ship on the sea surface to obtain a simulation database of the infrared polarization characteristics of the wake of a ship on the sea surface.

[0012] S5. Determine the original infrared polarization image of the ship's wake to be inverted, and solve for the ship's velocity inversion result based on the simulation database of the infrared polarization characteristics of the ship's wake.

[0013] Furthermore, step S2 specifically includes:

[0014] S21. Establish a Kelvin wake height field model and a sea surface height field model. Superimpose the Kelvin wake height field model and the sea surface height field model to obtain a sea surface ship wake height field model.

[0015] S22. Determine the simulated navigation conditions, including wave height, navigation speed, draft, and seawater physical properties;

[0016] S23. Using CFD simulation, numerical simulation results of the ship wake height field at different speeds were obtained by simulating the ship wake height field model on the sea surface.

[0017] Furthermore, the Kelvin wake height field model is specifically as follows:

[0018] ;in, , Indicates the ship's speed. Represents gravitational acceleration. Indicates half the width of the hull. Indicates half the length of the hull. Indicates draft. This represents the angle between the wake wave and the direction of the ship's motion. Indicates coordinates as The Kelvin tail height corresponding to the tail portion.

[0019] Furthermore, the sea surface height field model is specifically as follows: ;in,

[0020] Indicates the number of frequency divisions. Indicates the number of directional segments; , , , Represents the first frequency domain of sea surface waves. One frequency, This represents the average wind speed at a height of 19.5m above sea level. , , ,

[0021] , , This represents the frequency corresponding to the peak value of the sea surface power spectrum curve. Indicates the first The propagation direction of each component wave relative to the coordinate system of the sea surface height field model The included angle of the axis, express The increment, express The increment; Indicates wave number; Represents a random phase, with values ​​ranging from ; Indicates coordinates as The height corresponding to the sea surface portion.

[0022] Furthermore, the infrared polarization transmission model of the ship's wake on the sea surface is specifically as follows: ;in:

[0023]

[0024]

[0025]

[0026] ;

[0027] in, Represents the Stokes vector. For strength, This refers to the proportion of vertically or horizontally polarized light. This indicates the proportion of polarized light that is polarized at a 45° angle to the vertical or horizontal direction. This indicates the proportion of circularly polarized light in polarized light; Indicates the radiation intensity of the wake. Indicates the intensity of incident light. This represents the occlusion function of an object's surface. and These are the angles between the incident ray direction, the reflected ray direction, and the normal to the macroscopic object's surface, respectively. and These are the azimuth angles of the incident ray and the reflected ray, respectively; ζ total This represents a model of the height field of a ship's wake at sea. This indicates the partial derivative operation. Represents the surface roughness constant of an object. , These are the vertical and horizontal components of Fresnel reflectance, respectively. This represents the angle between the plane ROZ, formed by the direction of the reflected light and the Z-axis, and the plane RON, formed by the direction of the reflected light and the normal to the micro-surface element. The Z-axis is the direction of the normal to the surface of the macroscopic object.

[0028] Further, step S4 specifically involves: substituting the numerical simulation results obtained in step S2 into the infrared polarization transmission model of the ship's wake on the sea surface, determining the normal direction of the macroscopic object surface to establish a transformation matrix, and then performing calculations based on the infrared polarization transmission model of the ship's wake to obtain simulation results of the wake's infrared polarization characteristics. Multiple simulations are performed for different ship speeds, zenith angles, and azimuth angles to establish a database of infrared polarization of the sea wake; wherein, the zenith angle includes... and Azimuth includes and .

[0029] Furthermore, step S5 specifically includes:

[0030] S51. Solve for the infrared polarization degree image of the ship's wake from the original infrared polarization image of the ship's wake.

[0031] S52. Mask the ship's hull in the infrared polarization degree image of the ship's wake on the sea surface to prevent it from affecting the inversion results.

[0032] S53. Extract the wake length and Kelvin arm angle, and extract the infrared polarization degree of the wake region.

[0033] S54. Perform speed inversion on the wake based on infrared polarization degree, query the sea surface wake infrared polarization database based on the extracted wake features, and generate an initial population of 50 individuals based on the database query results.

[0034] S55. Calculate the residuals between individuals in the initial population and the query results of the infrared polarization database of sea surface wakes, and set the reciprocal of the residuals as the retention rate of each individual.

[0035] S56. Retain the two individuals with the highest retention rates, sum the retention rates of the remaining individuals to obtain the total retention rate, and select 50% of the individuals with a probability based on the ratio of the individual's own retention rate to the total retention rate.

[0036] S57. Randomly select an intersection point and swap the intersection point of each individual with that of another individual;

[0037] S58. Set the individual mutation probability to 0.05, and generate a random perturbation at a mutation point on the mutated individual;

[0038] S59. Select individuals with speeds between 2 and 40 knots. Substitute the parameters of the selected individuals into the infrared polarization transmission model of the ship's wake on the sea surface for calculation. Compare the calculation results with the polarization degree of the input image and calculate the error rate. Set the reciprocal of the error rate as the fitness. If the fitness is greater than or equal to 10, output the speed inversion result. If the fitness is less than 10, return to the retention calculation stage and iterate the population again.

[0039] The beneficial effects of the method described in this invention are as follows:

[0040] (1) This invention proposes an inversion method for analyzing the ship's speed based on the infrared polarization characteristics of the ship's wake. By utilizing the difference between the infrared polarization characteristics of the ship's wake and the infrared polarization characteristics of the surrounding sea surface, the infrared polarization characteristics of the wake are detected and analyzed, thereby improving the visibility and recognizability of the ship's wake.

[0041] (2) Construct an infrared polarization transmission model of ship wakes on the sea surface based on the infrared polarization degree of ship wakes. The correlation mechanism between ship speed and infrared polarization characteristics is explained through theoretical analysis. Furthermore, the speed inversion result corresponding to any original infrared polarization image of ship wakes on the sea surface is obtained through inversion. This solves the problem that ship wakes are difficult to effectively identify ship speed when the temperature difference between the wake and the sea surface is small.

[0042] This invention can be applied in practical fields of marine exploration. Attached Figure Description

[0043] Figure 1 This is a flowchart of the method described in an embodiment of the present invention;

[0044] Figure 2 This is a numerical simulation result of the height field of the wake of a ship on the sea surface in an embodiment of the present invention;

[0045] Figure 3 This is a diagram illustrating the effect of the degree of polarization of the wake in the simulation of the infrared polarization characteristics of the wake of a ship on the sea surface in an embodiment of the present invention.

[0046] Figure 4 This is a flowchart illustrating the process of obtaining the velocity inversion results of ships on the sea surface based on the simulation database of infrared polarization characteristics of ship wakes in this embodiment of the invention. Detailed Implementation

[0047] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0048] Example 1

[0049] like Figure 1 The diagram shows a flowchart of the ship speed inversion method based on the infrared polarization characteristics of wakes according to the present invention. The method includes the following steps:

[0050] S1. Use 3D modeling software to create a 3D model of the fluid domain of the ship's wake on the sea surface;

[0051] S2. Establish a height field model of the ship's wake on the sea surface, use a three-dimensional model of the fluid domain of the ship's wake on the sea surface to simulate the ship's navigation, and use CFD simulation to obtain numerical simulation results of the height field of the ship's wake at different speeds.

[0052] S3. Combine the height field model of the wake of a ship on the sea surface with the micro-element polarization bidirectional reflection distribution function PG model to establish an infrared polarization transmission model of the wake of a ship on the sea surface.

[0053] S4. Substitute the numerical simulation results obtained in step S2 into the infrared polarization transmission model of the wake of a ship on the sea surface to obtain a simulation database of the infrared polarization characteristics of the wake of a ship on the sea surface.

[0054] S5. Determine the original infrared polarization image of the ship's wake to be inverted, and solve for the ship's velocity inversion result based on the simulation database of the infrared polarization characteristics of the ship's wake.

[0055] Example 2

[0056] This embodiment further defines embodiment 1 and provides a further explanation of step S2. Step S2 specifically involves:

[0057] S21. Establish a Kelvin wake height field model and a sea surface height field model. Superimpose the Kelvin wake height field model and the sea surface height field model to obtain a sea surface ship wake height field model.

[0058] S22. Determine the simulated navigation conditions, including wave height, navigation speed, draft, and seawater physical properties;

[0059] S23. Using CFD simulation, numerical simulation results of the ship's wake height field at different speeds were obtained through simulation using a ship wake height field model on the sea surface. Figure 2 The image shown is a numerical simulation result of the height field of the wake of a ship on the sea surface.

[0060] The Kelvin wake height field model is specifically as follows:

[0061] ;in, , Indicates the ship's speed. Represents gravitational acceleration. Indicates half the width of the hull. Indicates half the length of the hull. Indicates draft. This represents the angle between the wake wave and the direction of the ship's motion. Indicates coordinates as The Kelvin tail height corresponding to the tail portion.

[0062] The sea surface height field model is specifically as follows: ;in,

[0063] Indicates the number of frequency divisions. Indicates the number of directional segments; , , , Represents the first frequency domain of sea surface waves. One frequency, This represents the average wind speed at a height of 19.5m above sea level. , , ,

[0064] , , This represents the frequency corresponding to the peak value of the sea surface power spectrum curve. Indicates the first The propagation direction of each component wave relative to the coordinate system of the sea surface height field model The included angle of the axis, express The increment, express The increment; Indicates wave number; Represents a random phase, with values ​​ranging from ; Indicates coordinates as The height corresponding to the sea surface portion.

[0065] Example 3

[0066] This embodiment further defines embodiment 1 and provides further explanation of step S3.

[0067] The infrared polarization transmission model of the wake of a ship at sea is as follows: ;in:

[0068]

[0069]

[0070]

[0071] ;

[0072] in, Represents the Stokes vector. For strength, This refers to the proportion of vertically or horizontally polarized light. This indicates the proportion of polarized light that is polarized at a 45° angle to the vertical or horizontal direction. This indicates the proportion of circularly polarized light in polarized light; Indicates the radiation intensity of the wake. Indicates the intensity of incident light. This represents the occlusion function of an object's surface. and These are the angles between the incident ray direction, the reflected ray direction, and the normal to the macroscopic object's surface, respectively. and These are the azimuth angles of the incident ray and the reflected ray, respectively; ζ total This represents a model of the height field of a ship's wake at sea. This indicates the partial derivative operation. Represents the surface roughness constant of an object. , These are the vertical and horizontal components of Fresnel reflectance, respectively. The angle between plane ROZ, formed by the direction of reflected light and the Z-axis, and plane RON, formed by the direction of reflected light and the normal of the micro-surface element, is represented. The direction of the Z-axis is the direction of the normal of the macroscopic object surface. The macroscopic surface coordinate system is established with the normal of the macroscopic object surface as the Z-axis.

[0073] Example 4

[0074] This embodiment further defines embodiment 1 and provides further explanation of step S4. Step S4 specifically involves: substituting the numerical simulation results obtained in step S2 into the infrared polarization transmission model of a ship's wake on the sea surface, determining the normal direction of the macroscopic object surface to establish a transformation matrix, and then calculating based on the infrared polarization transmission model of the ship's wake to obtain simulation results of the wake's infrared polarization characteristics. Multiple simulations are performed for different ship speeds, zenith angles, and azimuth angles to establish a database of infrared polarization of the sea wake; wherein, the zenith angle includes... and Azimuth includes and .

[0075] The numerical simulation results of the ship wake height field model are input into the established infrared polarization transmission model of the ship wake, normalized, and appended to the normal line of the 3D model of the ship wake height field. Based on the numerical simulation results appended to the normal line, the 3D model of the ship wake height field is rendered in grayscale, outputting an infrared polarization effect image of the ship wake. The infrared polarization characteristics can be represented by the degree of linear polarization (DOLP) map and the angle of polarization (AOP), expressed as:

[0076] , .

[0077] like Figure 3 The image shown is a simulation of the infrared polarization characteristics of a ship's wake on the sea surface, illustrating the degree of wake polarization.

[0078] Example 5

[0079] This embodiment further defines embodiment 1 and provides further explanation of step S5.

[0080] like Figure 4 As shown, step S5 specifically involves:

[0081] S51. Solve for the infrared polarization degree image of the ship's wake from the original infrared polarization image of the ship's wake.

[0082] S52. Mask the ship's hull in the infrared polarization degree image of the ship's wake on the sea surface to prevent it from affecting the inversion results.

[0083] S53. Extract the wake length and Kelvin arm angle, and extract the infrared polarization degree of the wake region.

[0084] S54. Perform speed inversion on the wake based on infrared polarization degree, query the sea surface wake infrared polarization database based on the extracted wake features, and generate an initial population of 50 individuals based on the database query results.

[0085] S55. Calculate the residuals between individuals in the initial population and the query results of the infrared polarization database of sea surface wakes, and set the reciprocal of the residuals as the retention rate of each individual.

[0086] S56. Retain the two individuals with the highest retention rates, sum the retention rates of the remaining individuals to obtain the total retention rate, and select 50% of the individuals with a probability based on the ratio of the individual's own retention rate to the total retention rate.

[0087] S57. Randomly select an intersection point and swap the intersection point of each individual with that of another individual;

[0088] S58. Set the individual mutation probability to 0.05, and generate a random perturbation at a mutation point on the mutated individual;

[0089] S59. Select individuals with speeds between 2 and 40 knots. Substitute the parameters of the selected individuals into the infrared polarization transmission model of the ship's wake on the sea surface for calculation. Compare the calculation results with the polarization degree of the input image and calculate the error rate. Set the reciprocal of the error rate as the fitness. If the fitness is greater than or equal to 10, output the speed inversion result. If the fitness is less than 10, return to the retention calculation stage and iterate the population again.

Claims

1. A method for inverting ship speed based on the infrared polarization characteristics of a wake, characterized in that, The method includes the following steps: S1. Use 3D modeling software to create a 3D model of the fluid domain of the ship's wake on the sea surface; S2. Establish a height field model of the ship's wake on the sea surface, use a three-dimensional model of the fluid domain of the ship's wake on the sea surface to simulate the ship's navigation, and use CFD simulation to obtain numerical simulation results of the height field of the ship's wake at different speeds. S3. Combine the height field model of the wake of a ship on the sea surface with the micro-element polarization bidirectional reflection distribution function PG model to establish an infrared polarization transmission model of the wake of a ship on the sea surface. S4. Substitute the numerical simulation results obtained in step S2 into the infrared polarization transmission model of the wake of a ship on the sea surface to obtain a simulation database of the infrared polarization characteristics of the wake of a ship on the sea surface. S5. Determine the original infrared polarization image of the ship's wake to be inverted, and solve for the ship's velocity inversion result based on the simulation database of the infrared polarization characteristics of the ship's wake.

2. The ship speed inversion method based on the infrared polarization characteristics of the wake as described in claim 1, characterized in that, Step S2 is as follows: S21. Establish a Kelvin wake height field model and a sea surface height field model. Superimpose the Kelvin wake height field model and the sea surface height field model to obtain a sea surface ship wake height field model. S22. Determine the simulated navigation conditions, including wave height, navigation speed, draft, and seawater physical properties; S23. Using CFD simulation, numerical simulation results of the ship wake height field at different speeds were obtained by simulating the ship wake height field model on the sea surface.

3. The ship speed inversion method based on the infrared polarization characteristics of the wake as described in claim 2, characterized in that, The Kelvin wake height field model is specifically as follows: ;in, , Indicates the ship's speed. Represents gravitational acceleration. Indicates half the width of the hull. Indicates half the length of the hull. Indicates draft. This represents the angle between the wake wave and the direction of the ship's motion. Indicates coordinates as The Kelvin tail height corresponding to the tail portion.

4. The ship speed inversion method based on the infrared polarization characteristics of the wake as described in claim 3, characterized in that, The sea surface height field model is specifically as follows: ;in, Indicates the number of frequency divisions. Indicates the number of directional segments; , , , Represents the first frequency domain of sea surface waves. One frequency, This represents the average wind speed at a height of 19.5m above sea level. , , , , , This represents the frequency corresponding to the peak value of the sea surface power spectrum curve. Indicates the first The propagation direction of each component wave relative to the coordinate system of the sea surface height field model The included angle of the axis, express The increment, express The increment; Indicates wave number; Represents a random phase, with values ​​ranging from ; Indicates coordinates as The height corresponding to the sea surface portion.

5. The ship speed inversion method based on the infrared polarization characteristics of the wake as described in claim 4, characterized in that, The infrared polarization transmission model of the wake of a ship on the sea surface is specifically as follows: ;in: ； in, Represents the Stokes vector. For strength, This refers to the proportion of vertically or horizontally polarized light. This indicates the proportion of polarized light that is polarized at a 45° angle to the vertical or horizontal direction. This indicates the proportion of circularly polarized light in polarized light; Indicates the radiation intensity of the wake. Indicates the intensity of incident light. This represents the occlusion function of an object's surface. and These are the angles between the incident ray direction, the reflected ray direction, and the normal to the macroscopic object's surface, respectively. and These are the azimuth angles of the incident ray and the reflected ray, respectively; ζ total This represents a model of the height field of a ship's wake at sea. This indicates the partial derivative operation. Represents the surface roughness constant of an object. , These are the vertical and horizontal components of Fresnel reflectance, respectively. This represents the angle between the plane ROZ, formed by the direction of the reflected light and the Z-axis, and the plane RON, formed by the direction of the reflected light and the normal to the micro-surface element. The Z-axis is the direction of the normal to the surface of the macroscopic object.

6. The ship speed inversion method based on the infrared polarization characteristics of the wake as described in claim 5, characterized in that, Step S4 specifically involves: substituting the numerical simulation results obtained in step S2 into the infrared polarization transmission model of a ship's wake on the sea surface, determining the normal direction of the macroscopic object surface to establish a transformation matrix, and then performing calculations based on the infrared polarization transmission model of the ship's wake to obtain simulation results of the wake's infrared polarization characteristics. Multiple simulations are performed for different ship speeds, zenith angles, and azimuth angles to establish a database of infrared polarization of the sea surface wake; where the zenith angle includes... and Azimuth includes and .

7. The ship speed inversion method based on the infrared polarization characteristics of the wake as described in claim 6, characterized in that, Step S5 is as follows: S51. Solve for the infrared polarization degree image of the ship's wake from the original infrared polarization image of the ship's wake. S52. Mask the ship's hull in the infrared polarization degree image of the ship's wake on the sea surface to prevent it from affecting the inversion results. S53. Extract the wake length and Kelvin arm angle, and extract the infrared polarization degree of the wake region. S54. Perform speed inversion on the wake based on infrared polarization degree, query the sea surface wake infrared polarization database based on the extracted wake features, and generate an initial population of 50 individuals based on the database query results. S55. Calculate the residuals between individuals in the initial population and the query results of the infrared polarization database of sea surface wakes, and set the reciprocal of the residuals as the retention rate of each individual. S56. Retain the two individuals with the highest retention rates, sum the retention rates of the remaining individuals to obtain the total retention rate, and select 50% of the individuals with a probability based on the ratio of the individual's own retention rate to the total retention rate. S57. Randomly select an intersection point and swap the intersection point of each individual with that of another individual; S58. Set the individual mutation probability to 0.05, and generate a random perturbation at a mutation point on the mutated individual; S59. Select individuals with speeds between 2 and 40 knots. Substitute the parameters of the selected individuals into the infrared polarization transmission model of the ship's wake on the sea surface for calculation. Compare the calculation results with the polarization degree of the input image and calculate the error rate. Set the reciprocal of the error rate as the fitness. If the fitness is greater than or equal to 10, output the speed inversion result. If the fitness is less than 10, return to the retention calculation stage and iterate the population again.

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